GIFT   OF 


Lib, 


8C61  'IZWltfd 
A  'X  '  as  n  OBJ  AS' 


9114  ( 

U.  S.  DEPARTMENT   OF  AGRICULTURE, 

WEATHER    BUREAU. 


ON    THE 


NORTH  PACIFIC  SLOPE 


BY 


B.  S.  PAGUE,  Local  Forecast  Official, 

AND 

S.  M.  BLANDFORD,  Observer. 


Published  by  permission  of  PROP.  WILLIS  L.  MOORE,  Chief  of  Weather  Bureau. 


PORTLAND,  ORE. 

Weather  Bureau  Print. 

1897. 


U.  S.  DEPARTMENT   OF  AGRICULTURE, 

WEATHER    BUREAU. 


ON    THE 


NORTH   PACIFIC  SLOPE 


BY 


B.  S.  PAGUE,  Local  Forecast  Official, 

AND 

S.  M.  BLANDFORD,  Observer. 


Published  by  permission  of  PROF.  WILLIS  L.  MOORE,  Chief  of  Weather  Bureau. 


PORTLAND,  ORE. 

Weather  Bureau  Print. 

1897. 


PKEFACE. 


FOR  the  purpose  of  placing  in  a  comprehensive  form 
the  subject  of  storm  development  and  movement,  and  the 
methods  of  forecasting  the  weather  on  the  Pacific  Coast, 
this  little  pamphlet  is  published.  It  is  believed  that  the 
method  of  presenting  to  the  mind  of  the  layman  the  sub- ' 
ject  by  means  of  charts  is  the  best.  There  are  many  false- 
theories  prevalent  in  the  mind  of  the  public  concerning 
storms  in  general.  A  lucid  explanation  of  **cepted  theory 
concerning  the  Pacific  Coast  weather  is  contained  herein.  ^ 
Especial  attention  is  invited  to  the  explanation  of  "Chi- 
nook" winds  on  page  10. 

Weather  Forecasting  in  all  portions  of  the  globe  is  a 
difficult  problem,  but  in  no  place  is  it  more  difficult  than 
on  the  North  Pacific  Slope.  Storm  movements  are,  in 
some  instances,  regular,  and  again  erratic ;  the  regular 
movements  only  are  here  given. 

The  matter  contained  herein  was  prepared  by  Mr. 
B.  S.  PAGUE,  Local  Forecast  Official,  Weather  Bureau, 
Portland,  Oregon,  who  is  the  official  Weather  Forecaster 
for  the  Pacific  Northwest ;  and  by  Mr.  S.  M.  BLANDFORD, 
Observer,  Weather  Bureau,  who  for  five  years  has  been 
an  assistant  at  Portland,  Oregon. 

PORTLAND,  OREGON,  August  15,  1897. 


J/ 

o/* 


WEATHER  FORECASTING. 

By   B.  S.  PAGTJE. 

When  it  is  considered  that  more  interests  are  directly  affected  by  weather 
changes  than  by  any  other  factor  or  condition,  it  appears  strange  that  more 
attention  is  not  paid  by  the  people  to  the  study  of  the  weather. 

Forecasts  have  been  made  by  the  unscientific  and  by  the  scientific,  yet 
none  that  are  made  reach  that  degree  of  perfection  that  is  desirable. 
That  they  are  daily  of  more  value  and  that  their  accuracy  is  steadily 
increasing,  will  not  be  denied,  yet  much  study  and  investigation  is  necessary 
to  make  the  improvements,  both  as  to  accuracy  and  length  of  time  of  the 
forecast  that  is  desired.  The  old-time  almanac  contained  forecasts  of  the 
weather  which  were  relied  upon  by  many,  yet  those  forecasts  were  often- 
times based  on  less  data  than  mere  general  averages. 

^  Then  there  is  the  so-called  "weather  forecast"  issued  by  various  people, 
who  claim  them  to  be  based  on  the  position  of  various  planets.  These  fore- 
casts are  manifestly  inaccurate,  vague,  and  misleading,  and  should  one  of 
the  "planet"  forecasts  be  verified,  a  great  victory  is  claimed  for  the  fore- 
caster. These  forecasts  may  have  their  value,  but  they  have  certainly  not 
shown  it.  It  is  not  the  purpose  of  this  paper  to  discuss  the  forecasts  of 
people  who,  at  the  best,  and  under  the  most  charitable  construction,  can  be 
designated  by  the  word  "charlatan,"  yet  the  scientific  investigations  of  the 
U.  S.  Weather  Bureau  and  its  forecasts  issued  are  so  at  variance  with  those 
of  the  faker,  that  this  touching  of  the  subject  was  necessary. 

It  should  be  understood  that  the  weather  predictions  of  the  government 
and  other  scientific  bureaus,  made  for  a  day  or  two  in  advance,  are  simple  in 
principle,  depending  upon  well-recognized  physical  deductions,  and  partly 
upon  analogical  conclusions.  There  is  no  mystery  either  in  the  theory  or 
practice  of  such  predictions,  and  the  more  numerous  the  observing  stations, 
and  the  longer  the  work  is  continued,  the  more  accurate  will  become  the 
predictions. 

There  are  also  methods  of  making  predictions  for  a  long  time  in  advance 
which  are  scientifically  justifiable,  and  upon  which  considerable  reliance  may 
be  placed.  When  the  climatic  conditions  of  a  place  have  been  carefully 
recorded,  let  us  say,  for  every  month  for  a  long  time,  it  becomes  possible 
to  predict,  with  great  probability  of  accuracy,  that  certain  conditions  will 
prevail  in  any  subsequent  month;  that  there  will  be  so  much  rain,  or  snow, 
or  so  many  windy  days.  Such  predicting  is  merely  asserting  that  the  aver- 
age will  prevail.  Again,  from  collateral  observations  extending  over  a 
sufficiently  long  time,  certain  ill-defined  cycles  sometimes  appear  in  weather 
changes,  and  by  making  use  of  these  a  general  prediction  may  be  made  for 


\\KATIIKR    FORECASTING, 

any  future  time.  While  such  long-range  predictions  as  these  are  perfectly 
legitimate,  the  data  are  yet  insufficient  to  make  them  of  much  importance. 

There  are  other  weather  prophets  who  pretend  to  predict  for  the  future, 
for  weeks  and  even  months  ahead,  and  profess  to  do  so  by  specially,  often 
personally  discovered  laws,  or  by  methods  not  known,  at  least  not  appre- 
ciated, by  scientific  bureaus.  This  kind  of  prophecy  is  generally  as  baseless 
as  the  rain-making  claim,  and  should  be  entitled  to  no  more  consideration. 
Any  one  who  claims  to  have  discovered  definite  laws  in  the  changes  of  the 
weather  is  mistaken.  Any  one  who  claims  to  have  discovered  cycles  in  the 
weather  changes  from  a  few  observations  of  any  sort,  is  also  mistaken. 
The  whole  class  of  long-range  weather  predictions  professedly  b-^ed  upon 
the  conjunction  or  opposition  of  planets,  upon  the  eclipses  of  the  sun,  moon, 
or  other  celestial  bodies,  or  upon  the  observed  action  of  animal  nature,  are 
unworthy  of  attention.  In  general,  it  may  be  said  that  all  weather  pre- 
dictions not  based  upon  long,  systematic,  and  extended  observations  of  the 
weather,  are  unworthy  of  consideration,  and  when  any  one  is  found  making 
predictions  without  such  data,  he  is  simply  guessing. 

The  Weather  Bureau  issues  general  forecasts  from  Washington  City, 
Chicago,  111.,  San  Francisco,  Cal.,  and  Portland,  Oregon.  The  forecasts 
issued  from  the  centers  are  for  a  distinct  and  well-defined  territory,  and  for 
a  stated  and  stipulated  period  of  time  ranging  from  24  to  36  hours.  Under 
well-defined  conditions,  forecasts  are  issued  for  a  greater  period,  sometimes 
for  as  much  as  three  and  four  days.  Such  forecasts  are  exceptional  and  are 
only  issued  under  well-defined  conditions.  The  word  "forecast,"  as  used  by 
the  Weather  Bureau,  means  that  the  conditions  are  such  as  to  indicate  that 
the  weather  will  be  as  is  stated.  The  forecast  is  in  no  sense  a  prophecy,  as 
that  word  is  usually  and  technically  understood.  The  Bureau  issues  fore- 
casts based  on  the  current  weather  conditions.  By  study,  observation,  and 
experience,  the  forecast  official  knows  that  usually  certain  conditions  pro- 
duce certain  results.  The  deductions  the  forecaster  prepares  in  plain,  terse 
language,  and  they  are  then  issued  to  the  public. 

Weather  observations  are  made  at  5  A.  M.  and  5  P.  M.,  120th  meridian, 
or  Pacific  Coast  time;  as  soon  as  made,  these  observations  are  prepared 
in  cipher,  for  economy  and  accuracy,  and  are  at  once  telegraphed  to  certain 
centers,  all,  however,  going  direct  to  the  central  office  of  the  Bureau  in 
Washington  City.  As  soon  as  received  at  the  various  forecast  offices,  the 
reports  are  translated  and  charted,  and  the  forecasts  are  deduced.  The 
Weather  Bureau  forecasts  are  verified  from  85  to  90  per  centum — a  degree 
of  accuracy  very  commendable. 

There  is  no  section  of  the  North  American  continent  that  is  more  interesting 
to  study  and  that  will  be  more  fruitful  for  results  than  the  North  Pacific  Coast 
region,  extending  to  and  including  Alaska.  A  thorough  understanding  of 
the  meteorological  conditions  of  this  region  will  tend  to  explain,  to  a  great 
extent,  the  weather  changes  which  affect  the  climatic  conditions  of  the 
United  States.  It  has  been  the  privilege  and  pleasure  of  the  writer  to  study 
the  weather  of  the  Pacific  Slope  for  the  past  ten  years,  and  the  most  marked 
characteristics,  as  understood  by  him,  are  here  given  for  the  benefit  of  those 
who  may  be  interested. 


NORTH    PACIFIC    SLOPE.  O 

There  are  but  two  well-defined  or  marked  types  of  the  weather  on  the 
Pacific  Slope,  which  for  convenience  it  has  pleased  the  writer  to  term  as 
Winter  and  Summer  types.  These  two  parent  types  have  some  sixteen  mod- 
ifications, yet  there  are  distinct  family  resemblances  in  each.  It  is  acknowl- 
edged that  the  food  of  a  storm  is  heat  and  moisture— without  them  the 
storm  loses  energy  and  is  dissipated.  The  storm,  like  an  animal,  seeks  its 
focd,  to  enable  it  to  retain  life  or  energy  and  to  grow,  where  it  may  find  it 
with  as  little  trouble  as  possible.  A  storm,  again  like  an  animal,  can  con- 
tain only  so  much  food;  hence,  when  it  has  enough  it  moves;  when  the 
supply  is  too  great  it  also  moves.  It  has  been  found  taat  storm  areas  center 
during  the  winter  months  along  the  Washington  or  Vancouver  Island  Coasts; 
with  the  advance  of  Summer  and  the  increasing  heat,  they  retreat  to  the 
North.  The  rotation  of  the  earth  gives  all  areas  of  high  or  low  pressure  an 
easterly  movement;  hence  the  storm  area  retreating  from  an  over-supply 
of  focd  passes  during  the  Summer  season  eastward  about  the  latitude  of 
Sitka,  Alaska;  from  thence  it  moves  towards  the  Great  Lakes,  where  it  may 
obtain  more  food.  This  movement,  in  high  latitudes,  is  called  the  Summer 
movement  of  areas  of  low  pressure.  With  the  passage  of  the  summer  season 
and  the  increasing  cold  of  winter,  the  storm  areas  move  southward  again, 
seeking  their  food  supply  and  obtaining  it  about  the  50th  degree  north  lati- 
tude, and  125th  degree  west  longitude,  or  about  Vancouver  Island.  Here  it 
fattens,  as  it  were,  i.  e.,  gains  energy,  and  moves  eastward,  about  the  50th 
degree  north  latitude,  crossing  the  Rocky  Mountains  and  passing  into 
Alberta  or  Saskatchewan,  thence  to  the  Mississippi  Valley.  This  is  the 
Winter  movement  of  the  storm  area,  and  is  what  is  termed  the  Winter  type 
of  weather  conditions  on  the  Pacific  Slope.  These  Winter  conditions  are 
shown  in  several  forms,  in  Charts  Nos.  1,  2,  and  3,  on  the  following  pages. 

The  movements  of  the  low  or  storm  areas  having  been  briefly  described, 
according  to  the  idea  of  the  writer,  the  movements  of  the  areas  of  high 
pressure  will  now  be  briefly  outlined:  Off  the  Southwestern  Coast  of  Cali- 
fornia is  an  area  of  perpetual  high  pressure;  apparently  from  this  immense 
area  of  high  pressure  move  smaller  areas  of  high  pressure  in  a  northeasterly 
direction,  to  the  California  Coast,  about  Cape  Mendocino,  from  whence  they 
move  in  winter  slightly  to  the  north  of  east  to  Southern  Idaho,  where  they 
become  central,  sometimes  move,  but  usually  dissipate.  In  summer  these 
areas  of  high  pressure  move  northward  along  the  coast  to  about  Vancouver 
Island,  whence  they  move  easterly,  following  closely  the  path  of  the 
winter  lows,  crossing  the  Rocky  Mountains  thence  towards  the  Mississippi 
Valley.  This  latter  is  termed  the  Summer  type  of  the  weather  conditions, 
and  is  shown  in  charts  Nos.  4  and  5,  on  the  following  pages.  There  is 
another  movement  of  high  pressures,  almost  exclusively  confined  to  the 
winter  season.  These  winter  highs  move  from  the  north  of  Alberta  in  a 
southerly  direction,  sometimes  having  a  westerly  overflow  to  the  Pacific 
Slope,  but  more  often  moving  toward  the  Mississippi  Valley. 

These  highs  from  the  North  occasionally,  in  winter,  join  with  the  highs 
from  the  Pacific,  in  Northern  Utah  or  Southern  Idaho.  Areas  of  low 
pressure  rarely  move  south  of  the  Central  Oregon  Coast;  when  they  do, 
they  usually  develop  into  very  severe  storms  when  crossing  Arizona  and 


6  WKATHEB    FORECASTING. 

New  Mexico,  coming  into  the  influence  of  the  moist  air  from  the  Gulf  of 
Mexico.  On  December  20,  1895,  the  writer  prepared  a  short  sketch  of  the 
weather  conditions  of  1895,  which  was  published  in  the  Monthly  Weather 
Review,  the  official  publication  of  the  U.  S.  Weather  Bureau,  in  the  Novem- 
ber, 1895,  issue.  It  is  very  appropriate  to  reproduce  the  sketch  as  it  appeared 
in  that  publication. 

WEATHER  TYPES  OF  THE  NORTH  PACIFIC  SLOPE. 

There  are  two  distinct,  well-defined  types  of  weather  on  the  North 
Pacific  Slope,  viz.,  the  Summer  type  and  the  Winter  type.  These  are  illus- 
trated by  the  following  sketch  of  the  meteorology  of  1895: 

Cn  April  20th,  the  first  type  of  summer  weather  conditions  appeared 
over  the  North  Pacific  Slope,  viz.,  an  area  of  high  barometric  pressure  mov- 
ing northward  along  the  Coast  to  Northwestern  Washington,  and  thence 
eastward  over  the  State  of  Washington.  In  the  synopsis  of  April  20th  it 
was  officially  announced  at  Portland  that  the  conditions  which  would  prevail 
until  the  first  appearance  of  a  Winter  type  of  weather  would  be  more  in 
favor  of  fair  weather  than  of  rain,  for  it  had  been  observed  that  after  the 
first  appearance  of  a  pure  type  of  summer  conditions  there  is  seldom  a 
recurrence  of  the  Winter  type  until  the  autumn. 

The  spring,  summer  and  autumn  were  unusually  dry.  This  was  especially 
true  of  the  period  from  September  15  to  November  1,  which  was  the  driest 
recorded  in  the  history  of  this  portion  of  the  country  during  the  past  fifty 
years.  Experience  had  shown  that  no  general  or  continued  rain  would 
occur  until  the  first  appearance  of  the  winter  type  of  storms,  and  this 
knowledge  was  used  in  the  daily  forecasts  issuing  regularly  from  the 
Weather  Bureau  Office  at  Portland,  Oregon.  This  winter  type  finally 
appeared  on  the  morning  of  Tuesday,  November  12. 

On  Monday  morning,  November  11,  1895,  there  was  no  appearance  of  any 
storm  disturbance,  but  by  noon  of  that  day  the  rapid  fall  in  the  barometer 
indicated  the  approach  of  a  well-defined  disturbance,  and  from  the  evening 
reports  of  this  date  the  approaching  storm  was  forecast.  The  morning 
reports  of  November  12  showed  that  the  storm  area  was  central  over  North- 
western Washington  and  that  the  trough  of  the  depression  extended  north- 
eastward toward  British  Columbia,  thereby  indicating  the  probable  path  of 
the  storm.  Warnings  of  aproaching  rains  and  high  winds  had  been  issued 
on  the  evening  of  November  11,  or  from  twelve  to  twenty  hours  before 
the  storm  arrived.  The  morning  reports  of  November  12  showed  that  an 
area  of  high  barometer  was  approaching  from  the  southwest  toward  Cali- 
fornia. General  precipitation  occurred  over  Washington,  Oregon,  and  Idaho 
on  the  12th  and  13th,  and  heavy  gales  from  the  south  and  east  prevailed 
along  the  coast  of  Northern  Oregon  and  Washington. 

The  morning  reports  of  November  13  showed  that  the  low  was  now 
central  north  of  Eastern  Montana,  and  that  the  high  pressure  was  moving 
inland  over  Southern  Oregon  and  Northern  California.  The  morning  reports 
of  November  14  showed  the  low  area  in  about  the  same  position,  but  more 
distinctly  defined,  and  the  high  area  central  near  the  region  where  Oregon, 


NORTH    PACIFIC    SLOPE.  7 

Idaho,  Nevada,  and  Utah  come  nearest  together.  The  morning  reports  of 
the  15th  showed  the  high  over  Oregon  and  Northern  Nevada,  and  the  low 
slightly  east  of  its  position  of  the  previous  day. 

The  feature  to  which  attention  is  especially  called  is  the  passage  of  the 
low  eastward  over  Washington  and  the  formation  of  the  area  of  high  pres- 
sure. This  movement  of  the  low  and  formation  of  the  high  was  the  first 
of  the  kind  to  occur  in  the  autumn  of  1895,  and  indicated  that  the  wet  or 
winter  season  had  set  in  over  the  North  Pacific  Slope. 

The  conditions  under  which  areas  of  high  pressure  form  and  move  are 
those  under  which  Chinook  winds  are  formed  over  the  Northwestern  portion 
of  the  United  States.  As  the  low  pressure  passes  to  the  north  and  the 
movement  of  the  wind  is  from  the  high  on  the  south  and  southwest  to  the 
low  on  the  northeast  side  of  the  mountains,  therefore  the  air  flowing  down 
the  mountain  sides  is  dynamically  heated. 

That  the  high  pressure  produced  the  rise  in  the  temperature  and  the 
wind  called  Chinook  in  the  present  case  is  shown  by  the  following: 

On  the  morning  of  November  12,  the  barometer  at  Portland  was  29.86, 
the  temperature  36°;  on  the  morning  of  the  15th  the  barometer  was  30.62, 
and  the  temperature  56°,  a  rise  in  pressure  of  0.76  of  an  inch  and  a  rise  of 
20°  in  the  temperature.  At  Roseburg  the  rise  in  the  barometer  was  0.72 
of  an  inch,  and  the  temperature  rose  16°;  at  Seattle  the  barometer  rose  0.72 
of  an  inch,  and  the  temperature  16°;  at  Baker  City  the  barometer  rise  0.66 
of  an  inch,  and  the  temperature  12°;  at  Spokane  the  barometer  rose  0.42 
of  an  inch,  and  the  temperature  rose  26°;  at  Helena  the  barometer  rose  0.20 
of  an  inch,  and  the  temperature  30°.  Chinook  winds  occurred  in  Montana 
on  November  16  and  17. 

The  following,  from  the  November  report  of  the  Montana  State  Weather 
Service,  may,  in  this  connection,  be  of  interest: 

A  cold  wave  signal  having  been  ordered  for  that  date  (November  17), 
and  the  weather  at  the  time  of  receipt  of  order  being  very  warm  and 
pleasant,  the  observer  (Mr.  R.  M.  Crawford,  at  Helena)  decided  to  pay  more 
than  ordinary  attention  to  the  expected  change.  About  3:30  P.  M.,  the 
wind,  which  had  been  blowing  gently  from  the  north,  veering  at  times  to 
the  northeast,  with  a  velocity  of  about  9  miles  an  hour,  stiffened  quickly 
and  came  directly  from  the  north,  lowering  the  temperature  6°  in  less  than 
five  minutes. 

The  indications  were  that  the  temperature  would  fall  much  lower,  but 
suddenly  dark,  vaporous-looking  clouds  appeared  in  the  extreme  southwest; 
with  them  simultaneously  a  strong  gale  from  the  same  quarter,  blowing 
at  the  rate  of  at  least  40  miles  an  hour.  The  gale  seemed  to  meet  the 
wind  coming  in  from  the  north,  and  drove  it  in  a  whirl  directly  toward  the 
northeast,  across  the  prairie,  in  a  funnel-shaped  cone,  plainly  perceptible  for 
a  long  distance  by  the  dust  gathered.  The  temperature  quickly  rose  to  58°, 
the  maximum  recorded  for  this  date,  and  the  Chinook  had  mastered  the  cold 
wave. 

Under  some  circumstances,  a  rise  from  0.25  to  0.75  inch  in  pressure  will 
produce  colder  weather,  but  under  other  conditions,  such  as  those  that 
prevailed  on  this  occasion,  a  rise  in  pressure  will  produce  a  rise  in  temper- 


s 


WEATHER    FORECASTING. 


ature,  or  Chinook  winds,  over  the  northwest  portions  of  the  United  States. 
The  rise  in  temperature  in  the  latter  case,  accompanying  a  rise  in  pressure, 
can  only  be  ascribed  to  dynamic  heating. 

The  following  table,  showing  pressure  and  temperature  at  8  A.  M.,  75th 
meridian  time,  from  November  8  to  18,  inclusive,  at  the  regular  Weather 
Bureau  Stations,  in  the  region  now  under  consideration,  illustrates  the  con- 
ditions prevailing  during  the  first  Chinook  in  the  autumn  of  1895: 


1 

Portland. 

Roseburg. 

Seattle. 

Baker  City. 

Spokane. 

Helena. 

' 

5 

» 

g 

3 

g 

9 

g 

9 

cd 

S 

g 

3 

i 

5 

o 

3 

•t 

3 

P 

3 

-j 

• 

PI 

1 

r 

j 

': 

i 

•o 

j 

F 

i 

*? 

i 

tJ 

8. 
9. 
10. 

30.36 
30.16 
30.12 

34 
34 

48 

30.34 
30.18 
31.14 

26 
32 
46 

30.36 
30.10 
30.02 

46 
42 
48 

30.32 
30.26 
30.04 

30 
26 
34 

30.42 
30.26 
30.04 

32 
32 
36 

30.30 
30.30 
30.22 

34 
28 
26 

11. 

30.36 

36 

30.30 

36 

30.32 

40 

30.22 

32 

30.32 

30 

30.28 

28 

12. 

29.86 

36 

29.90 

38 

29.98 

40 

29.96 

20 

30.02 

24 

30.10 

24 

13. 

30.34 

44 

30.40 

36 

30.26 

40 

30.34 

20 

30.30 

32 

30.12 

34 

14. 

30.40 

50 

30.48 

46 

30.28 

54 

30.38 

32 

30.32 

42 

30.32 

42 

15. 

30.62 

56 

30.62 

52 

30.50 

56 

30.62 

32 

30.44 

50 

30.30 

54 

16. 

30.58 

46 

30.52 

48 

30.56 

48 

30.60 

28 

30.50 

42 

30.32 

50 

17. 

30.32 

44 

30.30 

42 

30.26 

48 

30.38 

32 

30.18 

40 

30.08 

44 

18. 

30.36 

44 

30.30 

42 

30.36 

50 

30.32 

30 

30.26 

38 

30.00 

50 

1 

In  the  same  issue  of  the  Monthly  Weather  Review  appeared  the  following: 


LONG-RANGE    FORECASTS    IN    OREGON. 

The  following  extract  from  the  weather  synopsis  and  general  forecast  by 
Mr.  B.  S.  Pague,  Local  Forecast  Official  at  Portland,  Or.,  was  published  on  his 
morning  weather  map  for  November  12,  1895: 

"The  first  storm  of  the  season  is  shown  on  the  map  this  morning.  The 
conditions,  as  shown,  are  those  peculiar  to  the  winter  season  and  represent 
the  passage  of  the  dry  season  and  the  appearance  of  the  wet  season.  On 
April  20th  last,  the  first  type  of  summer,  dry  conditions,  appeared. 

"It  was  then  stated  that  from  this  date,  April  20th,  the  rain  would  be  light 
and  of  a  local,  more  than  a  general,  nature.  The  conditions  from  April  20th 
to  date  show  how  well  the  remarks  then  made  were  verified.  The  phenomenal 
dry  season,  which  has  prevailed  over  the  Pacific  Northwest  for  the  past  six 
weeks,  was  due  to  the  storm  areas  passing  from  the  north,  east  of  the  Rocky 
Mountains,  to  the  southeast,  toward  the  Great  Lakes;  usually,  the  storm 
areas  have  this  movement  during  the  months  from  June  to  the  middle  of 
September,  when  they  assume  their  winter  course,  and  move  southward 
along  the  coast  line,  striking  land  about  Vancouver  Island,  then  moving 
eastward,  or  at  times  move  in  other  directions.  The  period  of  dry  weather 
is  now  over;  it  is  probable  that  short  periods  of  fair  weather  may  prevail, 
but  it  is  not  probable  that  any  extended  period  of  fair  weather  will  again 
prevail  until  next  spring.  Since  April  20th  last,  the  conditions  were  more 
in  favor  of  dry  weather  than  of  wet  weather;  from  now  on  the  reverse  of 
this  will  be  true. 

"The  precipitation  over  the  Pacific  Northwest,  since  January  1,  has  been 
about  30  per  cent  deficient,  and  it  is  reasonable  to  assume  that  for  the  remain- 
der of  the  year  there  will  be  an  excess.' 


NORTH    PACIFIC    SLOPE.  9 

(Note — By  Editor  of  Monthly  Weather  Review). — The  importance  of  long- 
range  predictions,  especially  when  based  upon  a  broad  study  of  atmos- 
pheric conditions  over  the  whole  globe,  cannot  be  overestimated.  The 
changes  in  the  course  of  storm  tracks  may  be  spoken  of  as  either  the  cause 
or  the  concomitant  of  changes  in  the  weather  and  climate.  In  a  narrow 
sense  they  are  the  cause,  but  in  a  broader  sense  they  may  often  be  con- 
sidered as  simply  accompanying  or  correlated  phenomena.  The  weather  on 
the  immediate  coast  of  Oregon  and  Washington  depends  so  largely  upon 
What  is  called  the  general  circulation  of  the  atmosphere  over  the  North  ana 
South  Pacific  Oceans  that  it  may  be  reasonably  hoped  that  the  study  of 
this  latter  subject  will  elucidate  the  matter  and  render  these  seasonal 
forecasts  highly  accurate  and  satisfactory.) 

Long-range  weather  forecasts  are  only  possible  if  made  on  the  lines  sug- 
gested by  the  Editor,  Prof.  Cleveland  Abbe,  of  the  Monthly  Weather  Review. 
It  appears  to  the  writer  that  no  section  of  the  country  affords  a  more 
fruitful  field  for  investigation  than  the  Pacific  Northwest  to  determine  the 
laws  governing  storms,  their  development  and  movements.  The  investigation 
so  far  enables  an  accurate  forecast  to  be  made  of  winter  and  summer 
conditions,  as  has  been  shown  on  the  preceding  pages.  With  the  extension 
of  telegraphic  communication  to  Alaska,  and  meteorological  reports  there- 
from, a  great  advance  will  be  made  in  the  accuracy  of  all  forecasts,  and  the 
length  of  time  the  forecast  is  for.  A  more  thorough  study  may  make  it 
possible  to  determine  in  at  least  a  general  way  the  probable  weather  during 
the  prevalence  of  the  Winter  and  Summer  types.  These  are  results  that  are 
hoped  for.  and  the  writer  expects  to  see  realized. 

The  change  from  Summer,  or  dry,  to  Winter,  or  wet,  conditions  is  heralded 
by  a  gradual  weaker  movement  of  the  high  areas  to  the  50th  or  52d  degree 
north  latitude,  and  a  more  distinct  southern  deflection  of  the  storm  areas 
to  those  latitudes,  until  finally  the  energy  of  the  highs  becomes  so  reduced 
that  they  move  northward  and  then  eastward  about  the  40th  degree  north 
latitude,  and  the  low  area,  moves  southward  to  about  the  50th  degree  north 
latitude.  The  information  can  then  be  issued  that  the  rainy  season  has 
commenced.  A  long  period,  i.  e.,  three  or  more  days,  of  rain  is  improbable 
until  these  conditions  first  appear,  and  then  when  the  movements  are 
reversed,  the.  lows  retreating  to  the  north,  and  the  highs  moving  northward 
to  the  50th  degree  north  latitude,  then  any  rainy  period  in  excess  of  three 
days  is  again  improbable.  These  facts  have  been  established  and  can  be 
recorded  as  the  first  rules  toward  long-range  forecasts. 

In  the  Winter  conditions,  as  has  been  before  noted,  areas  of  high  pressure 
appear  over  Alberta  and  move  southeastward  to  the  Dakotas,  thence  toward 
the  Great  Lakes.  In  its  southward  movement  it  overflows  the  mountains 
to  the  west,  when  there  is  an  area  of  low  pressure  central  about  the 
mouth  of  the  Columbia  River.  Under  these  conditions  cold  weather  and 
snow,  changing  to  fair,  cold  weather  over  Washington,  Oregon  and  Idaho, 
prevails,  and  then  the  low  or  storm  area  will  sometimes  move  southeastward 
over  California,  and  become  a  storm  of  great  energy  before  it  has  spent 
its  force.  Chart  No.  1,  on  the  following  pages,  shows  conditions  mentioned 
above.  An  examination  of  Chart  No.  1  will  show  what  the  writer  terms  the 


10  WEATHER    FORECASTING. 

"California  dip"  in  the  isobars  29.5  to  30.2,  i.  e.,  stretching  to  the  southeast 
of  the  low,  the  isobars  "dip"  toward  California  and  Nevada,  and  such  a 
formation  precedes  general  rain  in  California,  and  usually  indicates  the 
movement  of  the  entire  storm  in  the  direction  of  the  "dip."  While  Chart 
No.  1  shows  typical  rain  conditions,  yet  it  is  not  the  common  type  of  move- 
ments of  winter  low  or  storm  areas  which  prevail.  Conditions  shown  in 
Chart  No.  1  produce  temperatures  much  below  the  normal  over  Oregon  and 
Washington.  Charts  NOR.  2  and  3  are  the  more  common  types  of  winter 
storms.  Chart  No.  2  is  given  so  as  to  illustrate  the  conditions  in  which 
Chinook  winds  have  their  origin.  The  following  description  of  Chinook 
winds,  prepared  by  the  writer,  is  here  published,  for  the  first  time,  by 
permission  of  the  Chief  of  the  Weather  Bureau.  The  Chinook  wind  is 
known  to  all  residents  of  the  northwest  portion  of  the  United  States,  and 
few  agree  on  the  causes  and  origin  of  the  wind.  The  writer  feels  that  his 
explanation  will  stand  the  test  of  the  most  careful  investigation,  and  that 
the  ideas  advanced  will  be  accepted  as  the  true  explanation  of  this  ever- 
welcome  wind. 

CHINOOK  WINDS. 
(Study  Chart  No.  2  in  this  connection.) 

The  term  "Chinook  wind"  had  its  origin  from  the  tribe  of  Chinook 
Indians  (now  almost  extinct,  but  which  was  very  strong  and  powerful  some 
sixty  to  seventy-five  years  ago),  that  had  its  home  in  the  southwestern 
portion  of  Washington,  on  the  Columbia  River.  Local  historians  relate  how 
the  northwest  wind  in  the  winter  season,  being  the  harbinger  of  fair  weather, 
was  called  by  the  trappers  at  Astoria  "the  wind  from  over  Chinook  camp." 

As  the  trappers  scattered  to  the  east  of  the  Cascades,  they  occasionally 
encountered  a  warm  southerly  wind  which  gradually  assumed  the  name  of 
Chinook  wind.  It  was  so  named  from  its  mildness,  resembling  to  an  extent 
the  mild,  balmy  wind  from  over  Chinook  camp.  As  the  trappers  spread 
over  the  northwestern  portion  of  the  United  States,  the  warm  southerly 
wind  of  winter  continued  to  be  called  by  them  "Chinook  wind,"  until  the 
term  became  common,  and  was  finally  accepted  by  meteorologists. 

The  term  was  first  used,  so  far  as  research  among  the  files  of  the  Monthly 
Weather  Review,  published  by  the  U.  S.  Meteorological  Service, 'Washington, 
D.  C.,  in  connection  with  the  warm,  south,  southwest,  west,  northwest  and 
sometimes  north,  winds  in  Montana. 

To  the  earlier  extension  of  the  military  telegraph  lines  in  Montana  than 
in  Washington  and  Oregon,  is  due  the  fact  that  the  term  Chinook  was  first 
applied  to  the  warm  winds  of  Montana.  The  operators  or  observers  employed 
on  these  telegraph  lines  vsed  the  local  common  name  applied  to  the  wind 
by  the  stockmen  in  their  reports.  The  name  was  thus  first  applied  to  the 
wind  in  Montana,  and  yet  to  a  large  extent  some  njeteorologists  are  of  the 
opinion  that  the  Chinook  winds  are  only  east  of  the  Rocky  Mountains,  and 
the  name  is  erroneously  applied  to  warm  southerly  winds  in  winter  to  the 
west  of  the  Rocky  Mountains. 

As  the  term  had  its  oiigin  west  of  the  Rocky  Mountains,  really  to  the 
west  of  the  Cascades,  the  writer  maintains  that  the  term  "Chinook  wind" 


NORTH    PACIFIC    SLOPE.  11 

can  be  and  is  properly  applied  to  the  warm  southerly  winds  of  winter  west 
of  the  Rocky  and  Cascade  Mountains.  The  Chinook  is  more  readily  observed 
in  Montana  and  to  the  north  thereof,  due  to  the  preceding  low  temperature 
and  the  rapid  and  marked  rise  produced  by  the  Chinook,  though  marked 
rises  in  temperature  west  of  the  Rocky  and  west  of  the  Cascade  Mountains 
are  frequently  observed.  In  the  American  Meteorological  Journal,  Vol.  3, 
p.  469,  is  to  be  found  the  following  definition  of  a  Chinook:  "Warm,  dry, 
westerly,  or  northerly  winds,  occurring  on  the  eastern  slopes  of  the  mountains 
of  the  Northwest,  beginning  at  any  hour  of  the  day,  and  continuing  from 
a  few  hours  to  several  days."  This  definition  is  perfectly  correct  so  far  as 
it  goes;  but  the  writer's  idea  of  the  definition  of  a  Chinook  is:  A  warm, 
dry,  or  moist  wind  from  the  southeast,  south,  or  southwest,  west  of  the 
Rocky  Mountains,  and  from  the  southwest,  west,  or  northwest,  to  the  east 
of  the  Rocky  Mountains,  beginning  at  any  hour  of  the  day  or  night,  and 
continuing  from  a  few  hours  to  several  days.  Such  definition  is  more  in 
accord  with  the  causes  which  produce  these  warm  winds  and  agrees  with 
the  original  application  of  the  term  as  understood  by  those  who  originated 
or  created  it. 

Chinook  winds,  according  to  the  writer's  definition  of  the  term,  only 
occur  under  one  kind  of  atmospheric  condition,  and  without  this  condition 
Chinooks  are  impossible. 

Preceding  a  Chinook,  by  from  two  to  six  days,  an  area  of  low  barometric 
pressure  is  along  tho  Washington  or  Oregon  Coast,  and  an  area  of  high 
barometric  pressure  overlies  Montana  and  the  British  provinces  to  the 
north.  This  area  of  high  pressure  has  low  temperatures,  from  10°  to  20° 
below  zero.  The  position  of  these  two  opposite  atmospheric  conditions 
produces  north  to  east  winds  over  Idaho,  Washington,  and  Oregon,  and  the 
temperature  decreases  and  snow  falls  to  the  east  of  the  Cascades,  extending 
over  Idaho  and  Montana,  and  sometimes  to  the  west  of  the  Cascades.  At 
the  end  of  about  three  days  the  high  pressure  moves  southeastward  to  the 
Northern  Mississippi  Valley,  thence  to  the  Great  Lakes  and  on  eastward. 
When  the  high  pressure  begins  to  move,  the  low  pressure  along  the  coast 
advances  northward  to  about  the  50th  degree  north  latitude;  thence  along 
that  parallel,  or  near  to  it,  across  British  Columbia  and  Saskatchewan; 
thence  towards  the  Great  Lakes.  Coincident  with  the  northward  movement 
of  the  low  pressure  along  the  coast,  there  appears  along  the  Central  Cali- 
fornia Coast  an  area  of  high  pressure  which  rapidly  increases  in  density 
and  moves  east  and  northeastward  to  Northeastern  Nevada,  Northern  Utah, 
and  Southern  Idaho,  where  it  becomes  central  by  the  time  the  low  pressure 
is  moving  eastward  over  British  Columbia.  The  low  on  the  north  and  its 
passage  eastward  causes  the  air  to  move  from  the  high,  central  about  Salt 
Lake,  to  the  low.  Those  are  the  conditions  from  which  a  Chinook  results. 

Now,  the  elevation  of  the  land  where  the  high  is  central  is  much  greater 
than  that  of  the  land  where  the  low  is  crossing;  secondly,  the  high  baromet- 
ric pressure  indicates  a  greater  mass  of  air  extending  upward  from  the 
earth  to  a  much  greater  elevation  than  the  air  where  the  low  pressure  is 
located.  Hence,  in  the  movement  of  the  air  from  the  high  to  the  low  there 
is  a  great  decline,  and  in  making  this  descent  the  air  is  gradually  compressed, 


12  WEATHER    FORECASTING. 

and  with  the  compression  warmth  is  generated,  in  this  way  dynamically 
heating  the  air  as  it  reaches  the  lower  levels,  giving  the  first  warming  effects 
of  the  Chinook.  The  meeting  of  the  warmer  air  with  the  moist  air  of  the 
low  pressure  causes  condensation,  and  rain  is  the  result.  The  passage  of  the 
area  of  low  pressure  eastward  produces  general  precipitation,  and,  meeting 
the  mountains,  th«  moisture  which  the  air  contains  is  more  rapidly  con- 
densed, and  the  greater  portion  or  all  of  its  moisture  lost  on  the  windward 
side  of  the  mountains,  the  winds  to  the  east  of  the  mountains  being  warm 
and  dry,  and,  due  to  the  cyclonic  movement  of  the  air,  are  westerly  and 
northerly.  Moist  air  expands  during  its  rise  up  the  side  of  the  mountain, 
and  is  then  again  compressed  in  its  descent  without  having  any  heat 
added  or  withdrawn.  Furthermore,  if  the  expansion  and  subsequent  com- 
pression takes  place  without  the  precipitation  of  moisture,  the  air  will  reach 
the  same  level  on  the  leeward  side  of  the  mountain  at  the  same  temperature 
it  had  at  the  corresponding  level  on  the  windward  side.  When  precipitation 
has  occurred  the  air  v/ill  reach  the  summit  of  the  mountain  at  a  higher 
temperature  than  the  theoretical  rate  of  decrease  which  elevation  would 
assign  to  it,  and  in  this  changed  condition  the  initial  temperature  will  be 
reached  at  a  pressure  much  lower  than  the  initial  pressure.  Continuing  in 
its  descent,  the  original  level  will  be  reached  with  a  higher  temperature 
than  at  the  starting  point,  and  the  air  will  be  much  drier,  and  these  con- 
ditions will  be  more  marked  in  proportion  as  the  original  mass  of  air  is 
warm  and  moist  or  cold  and  dry.  It  will  be  thus  seen  that  the  definition 
of  the  Chinook  as  quoted  is  correct  so  far  as  it  relates  to  the  eastern  side 
of  the  Rocky  Mountains,  but  it  is  not  at  all  applicable  to  the  Chinook  to  the 
west  of  the  Rocky  Mountains. 

Many  persons,  residents  of  the  country  affected  by  Chinook  winds,  are 
of  the  opinion  that  they  come  from  the  warmth  of  the  Japan  Gulf  currents, 
but  such  is  not  the  case.  Chinooks  are  not  warm  winds  from  the  ocean,  but 
are  formed,  according  to  the  writer's  idea,  in  the  manner  outlined  above. 

In  the  November,  1895,  Monthly  Weather  Review,  p.  148,  the  following 
by  the  writer  hereof  appeared,  which  in  this  connection  may  be  of  inter- 
est and  value,  for  a  new  thought  is  advanced  relative  to  the  comparative 
mildness  of  the  winter  temperatures  over  Washington  and  Oregon: 

"It  is  not,  as  I  understand,  admitted  by  all  that  Chinook  winds  occur 
west  of  the  Cascades.  From  my  knowledge  of  conditions  over  the  Pacific 
Northwest,  I  maintain  that  perfect  forms  of  Chinooks  occur  west  of  the 
Cascades  and  Rocky  Mountains.  The  degree  of  moisture  in  the  Chinook 
winds  varies  with  the  conditions  and  the  country  over  which  they  blow  (at 
Walla  Walla,  Wash.,  for  example,  sometimes  the  very  dry  Chinook  occurs, 
which  causes  the  snow  to  disappear  without  leaving  any  water  behind  it) ; 
again,  under  another  Chinook  the  snow  is  melted  and  little  evaporation  takes 
place.  The  explanation  of  this  is  as  follows:  In  the  first  case,  there  is 
little  or  no  movement  of  the  upper  currents  from  off  the  ocean,  hence 
the  expansion  and  heating  of  the  air  will  allow  dry  air  to  be  brought  into 
contact  with  the  snow  which  evaporates  as  it  melts.  In  the  second  case, 
there  is  a  decided  movement  of  air  from  the  ocean  inland,  and  the  dryness 
of  the  Chinook  is  overcome  by  the  vastness  of  the  supply  of  moist  air.  The 
Rocky  Mountains  bar  the  moist  air,  and,  therefore,  to  the  east  of  the  Rockies 
the  dry  Chinook  usually  prevails. 


NORTH    PACIFIC    SLOPE.  13 

"From  November  to  March  the  mean  temperature  over  Washington  and 
Oregon  is  materially  higher  than  it  is  to  the  east  of  the  Rocky  Mountains 
over  the  country  having  the  same  latitude.  This  mild  winter  temperature 
is  generally  ascribed  to  the  proximity  of  the  ocean,  and  to  the  Japan  current. 
White  the  ocean  does  modify  the  otherwise  low  temperature,  yet  the  mean 
temperature  is  as  much  or  more  influenced  by  the  dynamic  heating  of  the 
air  of  Chinook  winds.  If,  during  the  winter  season,  the  low  is  off  the  Cali- 
fornia Coast,  the  cold  air  on  the  northeast  flows  southwestward  and  gives 
the  low  temperatures  over  Washington  and  Oregon;  if  the  low  is  passing 
eastward  over  British  Columbia,  and  a  high  is  central  about  Salt  Lake  City, 
then  the  dynamic  heating,  or  Chinook  wind,  prevails,  and  high  temperature 
occurs. 

"In  these  two  instances  the  oceanic  influence  is  only  indirect.  Compara- 
tively high  temperatures  also  occur  in  connection  with  lows  moving  from 
off  the  California  Coast  northward  along  the  Oregon  and  Washington  Coasts, 
gradually  extending  inland;  in  this  latter  case  the  oceanic  influence  on  the 
mean  temperature  is  of  direct  effect. 

"Low  mean  temperatures  occur  from  November  to  March,  when  the  lows 
are  fiequent  and  move  southward  along  the  Coast  to  the  Columbia  River 
cr  farther  south  (they  seldom  move  much  to  the  south  of  the  Columbia). 
Mean  temperatures  above  the  normal  occur  when  the  lows  pass  eastward  at 
a  high  latitude,  about  British  Columbia.  In  the  latter  case  the  Chinook  or 
dynamic  heating  prevails." 

WINTER    CONDITIONS. 

Chart  No.  3  is  a  typical  one  of  the  conditions  which  prevail  in  winter. 
It  is  a  beautiful  illustration  of  the  successive  movements  of  storm  areas, 
while  the  high  pressure  remains  central  over  Northern  Utah  and  evidently 
fed  from  the  permanent  high  off  the  Southwest  California  Coast. 

THUNDER    STORMS. 

Chart  No.  4  is  an  illustration  of  the  conditions  as  they  prevail  when 
thunder  storms  occur  over  Oregon,  Washington,  and  Idaho,  or  over  portions 
of  these  States.  Conditions  which  produce  thunder  storms,  as  a  rule,  orig- 
inate in  the  heated  valleys  of  California,  whence  the  storms  move  northeast- 
ward to  Southeastern  Oregon,  where  their  energy  is  fully  developed  and 
thunder  storms  result.  Under  these  conditions  high  pressures  are  present 
over  Northwestern  Washington  and  thunder  storms  are  more  usual  on  the 
west  and  northwest  side  of  the  areas  of  low  pressure  than  upon  any  other 
side  of  the  lows. 

SUMMER    CONDITIONS. 

Chart  No.  5  is  an  excellent  illustration  of  the  summer  conditions  over  the 
Pacific  Northwest.  The  area  of  low  pressure  is  shown  to  be  central  over 
Manitoba,  and  evidently  moved  from  the  ocean  eastward  about  the  57th 
degree  north  latitude,  and  southeastward  over  Alberta  to  its  present  position; 
it  is  now  a  dry  low,  but  may  develop  moisture  when  coming  within  the 
influence  of  the  humid  atmosphere  from  the  Great  Lakes. 

The  high  pressure  moved  northward  along  the  California  and  Oregon 
Coasts;  when  it  was  central  off  the  Northern  California  Coast,  cloudy  and 
foggy  weather  prevailed  o^er  the  western  portion  of  Oregon  and  Washington, 
with  slightly  lower  temperatures  and  scattered  showers.  When  the  high 


14  WEATHER    FORECASTING, 

became  central  over  Northwestern  Washington,  then  the  clouds  and  fog 
were  dissipated,  and  clear,  balmy,  ideal  weather  prevailed;  with  the  move- 
ment of  the  high  eastward  the  temperatures  increased,  and  when  it  was  cen- 
tral to  the  north  and  northeast  of  Northeastern  Washington,  very  warm 
weather  prevailed.  The  hot,  dry  winds  which  occasionally  damage  the  grain 
crop  of  Eastern  Washington  and  Eastern  Oregon  occur  when  the  high  is  in 
the  position  last  mentioned.  The  high  crosses  the  Rocky  Mountains,  and 
another  high  appears  off  the  California  Coast.  It  requires  from  five  to 
seven  days  for  the  high  to  appear,  make  its  north  and  then  eastward  move- 
ment, and  to  cross  the  Rocky  Mountains.  These  facts  being  known,  the 
writer  has  been  very  successful  in  making  forecasts  covering  periods  of 
about  one  week.  Such  forecasts  were  made  for  Washington,  Oregon,  and 
Idaho  during  the  3ummer  season  of  1895  and  1896,  and  the  result  warrants 
further  efforts  in  this  line. 

THE   WEATHER   MAPS. 

The  Weather  Maps  issued  from  the  U.  S.  Weather  Bureau  Station  in 
Portland,  Or.,  present  an  outline  map  of  the  United  States  from  the  Great 
Lakes  westward,  and  of  the  British  Possessions  to  the  north  of  the  western 
portion  of  the  United  States,  showing  the  stations  where  weather  observa- 
tions are  taken  daily  at  8  A.  M.  and  8  P.  M.,  seventy-fifth  meridian  time  (5  A. 
M.  and  5  P.  M.,  120th  meridian  time,  and  telegraphed  to  Washington, 
Portland,  Seattle,  and  other  cities.  These  observations  consist  of  read- 
ings of  the  barometer,  thermometer  (wet  and  dry),  direction  and  velocity 
of  wind,  state  of  sky  (whether  cloudy  or  otherwise),  and  amount  of  rain 
or  snow.  Solid  'lines,  called  isobars,  are  drawn  through  points  having  the 
same  pressure;  a  separate  line  being  drawn  for  each  difference  of  one-tenth 
of  an  inch  in  the  height  of  the  barometer.  Dotted  lines,  called  isotherms, 
connecting  places  having  the  same  temperature,  are  drawn  for  each  ten 
degrees  of  the  thermometer.  Heavy  dotted  lines,  inclosing  areas  where  a 
great  change  in  temperature  has  occurred  within  the  last  twenty-four  hours, 
are  sometimes  added.  The  direction  of  the  wind  is  indicated  by  an  arrow 
flying  with  the  wind,  or  opposite  to  the  ordinary  vane.  Shaded  areas  show 
where  rain  or  snow  has  been  falling  since  the  last  observation. 

The  general  movement  of  storms  is  from  west  to  east,  with  the  trend 
of  the  atmosphere,  which  moves  in  a  series  of  atmospheric  waves,  the  crests 
of  which  are  designated  on  the  maps  "highs"  and  the  troughs  or  depressions 
"lows."  The  storms  affecting  the  weather  on  the  North  Pacific  Coast,  as 
a  rule,  come  from  the  north.  The  winds  blow  spirally  inward  into  a  storm 
and  spirally  outward  fiom  an  area  of  high  pressure;  hence,  when  the  storm 
area  is  in  the  north,  the  winds  come  from  the  south,  and  as  the  storm  area 
moves  eastward  the  winds  veer  to  the  westward. 

There  are  two  distinct  types  of  weather  on  the  North  Pacific  Coast,  for 
convenience  called  the  Summer  and  Winter  types.  As  the  heat  of  summer 
increases,  the  storm  areas  retreat  to  the  north,  and  are  carried  eastward 
about  the  latitude  of  Sitka,  Alaska;  once  east  of  the  chain  of  mountains, 
they  do  not  again  materially  affect  the  weather  to  the  west,  but  move 


NORTH    PACIFIC    SLOPE.  15 

southeastward  toward  the  Great  Lakes,  and  thence  across  New  England  or 
down  the  St.  Lawrence  Valley  into  the  Atlantic  Ocean.  As  these  storm 
areas  retreat  to  the  northward,  the  rains  over  the  Pacific  Northwest  decrease, 
until  finally,  during  midsummer,  almost  absolute  dryness  prevails.  Occa- 
sional showers  prevail  in  summer,  sometimes  from  the  influence  of  the 
lows  passing  to  the  eastward  of  the  Rocky  Mountains,  their  influence  extend- 
ing to  the  westward;  more  frequently,  however,  the  occasional  summer 
showers  occur  from  thunder  storms.  These  storms  are  quite  rare  on  the 
Pacific  Northwest,  and  when  they  occur  are,  as  a  rule,  produced  from  a 
low  passing  to  the  northeast  from  the  Central  California  Valleys  toward 
Northern  Idaho.  The  thunder  storms  usually  occur  on  the  west,  northwest, 
and  north  of  these  lows.  As  the  heat  of  summer  decreases,  the  path  of  the 
lows  gradually  moves  southerly  until,  by  the  1st  of  November,  it  follows 
the  course  of  the  Japan  current  to  Vancouver  Island,  whence  the  storms 
pass  eastward,  following  quite  closely  the  international  boundary  line,  until 
the  eastern  side  of  the  Rocky  Mountains  is  reached,  when  their  course  is 
southeastward  toward  the  Great  Lakes.  With  the  southern  deflection  of 
the  storm  movements,  che  rains  increase  in  amount  and  frequency.  The 
greater  portion  of  the  rains  is  deposited  on  the  western  side  of  the  Coast 
Range  of  mountains;  and  about  two-thirds  as  much  is  deposited  between 
the  Coast  and  Cascade  Ranges.  In  the  passage  of  the  storm  area  over  the 
Cascade  Range,  the  air  is  forced  to  such  a  height,  and  so  much  of  its  moisture 
is  lost  by  this  action,  that  but  a  small  percentage  remains  to  be  deposited  on 
the  eastern  side  of  the  Cascade  Mountains. 

The  Summer  type  of  weather  consists  of  areas  of  high  pressure  moving 
northward  along  the  Coast  line  from  Cape  Mendocino  to  Vancouver  Island; 
thence  they  move  eastward,  following  closely  the  path  of  the  low  pressures 
in  winter.  With  the  approach  of  high  pressures  the  temperature  decreases, 
the  cloudiness  over  Washington  and  Oregon  increases,  and  occasionally  rain 
falls  west  of  the  Cascades;  fog  results  west  of  the  Cascades  when  the 
center  of  high  pressure  is  about  the  mouth  of  the  -Columbia  River.  The 
cloudiness  decreases  when  the  center  of  the  high  is  over  Puget  Sound,  and 
when  the  center  crosses  the  Cascade  Mountains  the  weather  becomes  clear 
and  the  temperature  rises.  The  highest  temperatures  occur  when  the  center 
of  the  high  has  passed  and  is  to  the  northeast  of  Spokane.  When  the  high 
pressure  first  appears  off  Cape  Mendocino,  cooler  weather  may  be  expected 
for  two  days,  then  one  day  of  stationary  temperature,  then  two  or .  three 
days  of  warmer  weather. 

In  the  winter  season  these  highs  pass  eastward  over  Southern  Oregon 
and  become  central  about  the  Great  Salt  Lake;  due  to  their  influence,  higher 
temperatures  prevail  to  the  north,  northwest,  and  northeast,  especially  dur- 
ing, or  after,  the  passage  eastward  of  a  storm  area  in  the  path  above  men- 
tioned. 

Areas  of  high  pressure  also  move  southerly  from  the  Arctic  Region  to 
the  north  of  Montana.  During  the  winter  season  these  high-pressure  areas 
frequently  retard  the  eastern  movement  of  the  storm  areas  from  Vancouver 
Island  or  the  Washington  Coast,  and  then  result  several  days  of  rain  west 
of  the  Cascades,  and  sometimes  snow  to  the  east  of  them.  When  the  high 


16  WEATHER    FORECASTING. 

pressure  area  is  sufficiently  large  and  dense,  and  the  temperatures  low,  the 
storm  areas  are  forced  south  of  the  Columbia  River;  the  cold  air  flows 
from  the  northeast,  and  then  results  heavy  snow  to  east  of  the  Cascades, 
and  occasionally  to  the  west  of  them.  During  the  winter  season  the  lows 
follow  each  other  in  quick  succession;  gales  prevail  along  the  coast,  and 
general  rain  results.  In  the  spring,  after  the  first  movement  of  high  pressure 
from  off  the  California  Coast  northward  to  Vancouver  Island,  thence  east- 
ward, the  winter  season  or  type  of  storm  is  at  an  end.  In  the  autumn,  after 
the  first  winter  type  of  storm  appears,  the  summer  types  cease. 

SENSIBLE   TEMPERATURES. 

EFFECT  OF  HEAT  ON  THE  BODY  IN  OREGON. 
By  B.  S.  PAOUE. 

Much  has  been  said  and  written  of  the  climate  of  Oregon,  of  its  lack  of 
sunshine,  its  rainfall,  its  temperature  and  of  all  phases  of  the  weather,  but 
seldom  is  anything  said  of  the  physiological  effect  of  the  heat  in  Oregon.  It 
is  well  known  that  on  account  of  its  long  sea  coast,  its  mountain  ranges  and 
its  great  plateau  region,  that  within  the  boundaries  of  the  State  may  be 
found  any  climate  that  may  be  desired,  save  that  of  the  semi-tropical  or 
tropical  type.  The  snow-capped  mountains  and  higher  mountain  regions 
-have  temperatures  equal  to  the  Arctic  region,  the  plateau  the  climate  of  Min- 
nesota and  Canada,  the  valleys  that  delightful  climate  peculiar  to  Virginia 
or  France.  The  greater  portion  of  the  State  has  a  pleasant  mean  tempera- 
ture, while  the  immediate  coast  has  a  climate  free  from  heat  and  free  from 
cold. 

Throughout  the  great  valley  of  the  Columbia,  over  the  greater  portion  of 
the  plateau  region  and  in  the  Rogue  River  Valley,  maximum  temperatures  of 
from  100°  to  108°  are  recorded  during  the  heat  of  summer.  These  high  tem- 
peratures would  be  sufficient  to  produce  heat  prostration  and  sunstroke,  were 
it  not  for  the  safeguards  which  nature  has  provided.  Temperatures  of  from 
85°  to  95°  are  recorded  every  summer  in  the  great  Willamette  Valley,  and  in 
the  Umpqua  Valley — these  two  valleys,  together  with  the  Rogue  River 
Valley,  comprise  what  is  called  Western  Oregon,  excluding  the  coast  region. 
Facetious  remarks  are  often  made  that  "it  rains  13  mouths  in  the  year  in 
Oregon."  The  name  applied  to  Oregonians  is  "Webfeet."  The  section  of  the 
United  States  having  the  greatest  cloudiness  is  the  northwestern  portion  of 
the  United  States,  decreasing  over  Western  Oregon,  while  over  Eastern 
Washington  and  more  especially  over  Eastern  Oregon  the  cloudiness  is  not 
so  great  as  over  the  thickly  settled  portion  of  the  country  surrounding  the 
Great  Lakes,  the  Atlantic  and  Gulf  Coast  States.  These  data  are  here 
inserted  to  enable  an  explanation  to  be  made  concerning  the  rainfall  and 
cloudiness  before  going  into  the  main  subject  of- this  paper.  The  sunshine  at 
Portland,  which  is  less  than  that  which  prevails  over  the  great  valleys 
between  the  Coast  and  Cascade  Ranges,  averages  35  per  centum  of  the  possi- 
ble. In  summer  the  actual  sunshine  ranges  as  high  as  65  per  cent,  of  the  pos- 
sible, while  in  winter  it  decreases  to  as  low  as  15  per  cent,  of  the  possi- 
ble. This  is  less  sunshine  than  that  which  prevails  over  the  greater  portion 


NORTH    PACIFIC    SLOPE.  17 

of  the  United  States.  As  vegetation  has  naturally  but  little  growth  during 
the  winter  months,  the  absence  of  sunshine  is  practically  no  detriment,  while 
in  the  spring,  summer  and  autumn,  during  the  growing  and  ripening  season, 
the  sunshine  is  fully  sufficient  for  all  needs,  whether  for  growtli,  physical 
comfort  or  pleasure.  The  rainfall  is  not  excessive  in  the  great  valleys,  for  it 
is  less  than  50  inches  annually.  Along  the  immediate  coast,  excessive  pre- 
cipitation, i.  e.,  65  inches  or  more,  occurs  almost  annually.  The  rainy  period 
might  be  so  called  from  October  15  to  March  15.  From  March  15  to  June  15, 
and  from  September  15  to  October  15,  showers  prevail.  From  June  15  to  Sep- 
tember 15,  the  real  summer  or  dry  season,  showers  are  rare.  Hence  it  is  seen 
that  the  facetious  remark  and  the  sobriquet  are  both  in  error.  From  Octo- 
ber 15  to  March  15,  a  period  of  150  days,  rain  falls  on  an  average  on  from  90 
to  100  days;  so  that,  even  during  the  mid-rainy  season,  the  number  of  days 
on  which  rain  falls  is  not  markedly  excessive.  However,  sufficient  in  this 
connection  to  state  that  the  death  rate  in  Oregon  is  the  smallest  of  any 
State  in  the  Union,  crops  always  mature  and  are  very  prolific,  hen^e  the 
climate  cannot  certainly  be  said  to  be  injurious,  but  rather  it  is  on  the  whole 
one  of  the  most  pleasant  and  delightful  that  can  be  found  anywhere  in  the 
whole  country,  and,  considering  all  things,  few  climates  in  the  world  equal 
it  for  its  many  pleasant  and  advantageous  features.  With  this  digression, 
the  real  subject  of  this  paper  can  now  be  more  intelligently  discussed. 

The  temperatures  noted  are  those  from  the  United  States  Weather  Bureau 
records,  and  show  the  temperature  of  the  air,  the  thermometer  being  in  the 
shade,  exposed  in  a  standard  thermometer  shelter.  The  reason  that  there 
are  fewer  injurious  effects  from  the  high  temperature  is  that,  while  the 
degree  of  heat  noted  is  that  which  is  actually  recorded,  due  to  causes  which 
will  be  explained,  the  temperature  affecting  animal  and  vegetable  life  may 
be  less. 

The  temperature  cf  living  bodies  is  influenced  by  temperature  of  air,  its 
moisture  and  its  rate  of  movement;  living  bodies  differing,  as  a  rule,  from 
inorganic  masses,  in  that  the  former  exude  constantly  a  more  or  less  variable 
amount  of  moisture  to  be  evaporated,  and  thereby  introduce  a  factor  in  ccol- 
ing  not  found  normally  in  the  latter  class  of  bodies,  i.  e.,  evaporation. 

By  sensible  temperature  is  meant  that  which  is  felt  at  the  surface  of  the 
skin.  The  body,  when  in  a  healthy  state,  is  constantly  furnishing  moisture 
to  the  skin,  which  stands  in  drops,  or,  as  they  are  called,  "beads  of  perspira- 
tion." This  moisture  is  evaporated  by  the  air.  The  cooling  effect  of  the 
evaporation  is  the  safeguard  against  injurious  effects  by  extreme  heat.  When 
water  is  changed  from  the  liquid  to  the  vapor  condition,  a  certain  quantity 
of  heat  is  utilized,  which  during  the  evaporation  is  changed  into  latent  heat, 
and  is  no  longer  sensible.  A  feeling  of  coldness  therefore  results  from  the 
change,  and  as  long  as  evaporation  continues,  the  surface  where  it  takes 
place  is  cooler  than  the  general  temperature  of  the  surrounding  air.  When 
one  is  heated,  a  fan  is  used  to  give  relief  and  make  one  more  comfortable. 
The  motion  of  the  fan  causes  a  more  rapid  movement  of  the  air;  this  air 
moved  by  the  fan  against  the  face  has  the  same  temperature  as  that  which 
is  not  disturbed.  The  cooling  effect  comes  from  the  more  rapid  evaporation 
of  moisture  from  the  face  and  exposed  portions  of  the  body,  and  from  the 


18 


WEATHER    FORECASTING. 


increased  convectional  loss  of  heat  caused  by  the  more  rapid  movement  of 
the  air.  This  lower  temperature,  felt  by  the  face  under  the  influence  of  the 
fanning,  is  the  sensible  temperature. 

Inasmuch  as  the  temperature  of  the  wet  bulb  thermometer  is  that  of  an 
evaporating  surface,  influenced  by  the  prevalent  meteorological  conditions,  in 
some  instances,  especially  when  the  atmospheric  temperature  is  very  high 
and  the  effusion  of  perspiration  consequently  great,  the  sensible  temperature 
will  in  all  probability  be  less  than  that  of  the  air,  and  greater  than  that  of 
the  wet  bulb  thermometer.  Perhaps  midway  between  would  be  as  fair  an 
approximation  as  could  be  made  in  the  present  state  of  our  climatologic 
knowledge.  For  that  reason  it  will  perhaps  assist  our  appreciation  of  cli- 
matic features  of  every  region  to  consider  the  temperature  of  the  wet  bulb 
thermometer  in  connection  with  that  of  the  air  thermometer.  The  following 
statement  of  average  air  and  wet  bulb  thermometer  readings  is  given  for 
Portland,  Oregon,  for  the  months  of  June  to  September  inclusive,  from 
readings  made  during  the  greatest  heat  of  the  day.  The  data  are  based  on 
10  years'  records: 


1» 

W. 

1* 

91. 

18 

92. 

18 

93. 

18 

M. 

18 

J5. 

18 

96. 

Months. 

> 
*T 

Wei  Ther- 
mometer. 

> 
f? 

Wet  Ther- 
mometer-. 

> 
n 

Wet  Ther- 
mometer. 

> 

*r 

Wet  Ther- 
mometer. 

> 
•i 

Wet  Ther- 
mometer. 

> 
n 

Wei  Ther- 
mometer. 

> 
•i" 

j 

Wet  Ther- 
mometer. 

June                .          .  . 

69 

59 

66 

56 

70 

57 

63 

54 

63 

55 

70 

57 

n 

56 

July    

75 

61 

78 

63 

73 

59 

74 

60 

77 

6fl 

74 

59 

80 

63 

August  

76 

6? 

SO 

65 

77 

6? 

76 

61 

79 

64 

75 

60 

73 

62 

September 

7? 

59 

67 

5S 

70 

60 

6? 

56 

66 

56 

6? 

5? 

69 

57 

In  this  table  it  is  seen  that  the  wet  thermometer  temperature  is  on  an 
average  about  14"  lower  than  the  air  temperature;  while  on  the  day  of 
extreme  high  temperature  mentioned  the  difference  was  33°,  and  this  differ- 
ence is  dependent  upon  the  amount  of  moisture  in  the  air.  If  the  air  were 
as  moist  as  that  found  in  the  region  of  the  Great  Lakes,  and  along  the  Atlan- 
tic seaboard,  and  the  temperature  as  high  as  it  now  is  at  times,  the  effect  of 
the  heat  might  be  injurious. 

Sunstrokes  are  produced  by  heat.  The  normal  temperature  of  a  healthy 
person  is  98.4°;  if  it  rises  above  99.5°  or  sinks  below  97.3°,  some  form  of  dis- 
ease in  indicated.  If  a  person  is  shown  to  have  a  temperature  of  106°,  the 
prognosis  is  unfavorable,  and  110°  is  almost  certain  to  be  fatal.  Hence  it 
can  be  seen  that  evaporation  is  absolutely  necessary  to  cool  the  body  during 
periods  of  very  high  temperature,  else  the  blood  becomes  heated  and  death 
ensues.  The  physiological  and  social  conditions  favorable  to  sunstroke  are, 
anxiety,  worry,  overwork,  irregularities  in  food,  overcrowding  and  bad  ven- 
tilation, and,  to  a  marked  degree,  intemperance.  One  using  beer,  whiskey, 
or  other  blood-heating  drinks,  is  much  more  predisposed  to  sunstroke  than 
one  using  pure  water.  Personal  uncleanliness,  which,  among  other  things, 


NORTH    PACIFIC    SLOPE.  19 

prevents  the  healthy  action  of  the  skin;  tight  garments,  which  impede  the 
functions  alike  of  the  heart  and  lungs,  and  living  in  overcrowded  and  unsani- 
tary dwellings,  have  an  equally  hurtful  tendency.  To  overcome  the  unpleas- 
ant and  debilitating  effects  of  heat,  as  much  as  possible,  it  is  necessary  to 
keep  a  clean,  healthy  skin,  to  avoid  alcoholic  drinks,  and  to  have  pure  food 
and  pure  air.  To  obtain  the  beneficial  effects  of  the  reduction  of  temperature 
by  evaporation,  the  shade  must  be  sought,  and  the  direct  rays  of  the  sun 
avoided.  Beneficial  effects  may  be  obtained  by  a  natural  or  artificial  breeze 
or  wind,  and  for  parts  of  the  body  covered  by  clothing  they  may  be  obtained 
by  adapting  the  clothes  to  the  free  passage  of  air  and  moisture.  For  hot 
weather  and  in  the  shade,  the  color  of  the  clothing  is  of  less  consequence 
than  the  texture,  together  with  sufficient  looseness  to  permit  of  the  free 
access  of  air. 


WEATHER    TYPES. 

By   S.  M.  BLANDFORD. 

One  of  the  duties  of  the  U.  S.  Weather  Bureau  is  the  charting  of  meteor- 
ological conditions,  and  the  issuing  of  forecasts.  On  the  Pacific  Coast  there 
are  two  places  where  general  forecasts  are  made.  Portland  and  San  Fran- 
cisco. The  territory  covered  by  the  forecasts  of  the  Portland  office  embraces 
Oregon,  Washington,  and  Idaho.  Twice  each  day  forecasts  are  made.  In 
case  severe  winds  on  the  coast  and  Sound  are  liable  to  occur,  forecasts  are 
sometimes  specially  made.  A  daily  chart  is  issued  each  day,  for  the  benefit 
of  the  public,  showing  the  weather  conditions,  position  of  the  storm,  etc.  It 
is  for  the  benefit  of  those  who  desire  to  study  the  daily  weather  charts  that 
five  distinct  types  of  the  weather  have  been  selected  for  publication.  In 
the  Eastern  States,  to  a  large  extent,  and  on  the  Pacific  Coast  quite  gen- 
erally, the  people  aie  making  many  valuable  uses  of  the  information  fur- 
nished in  the  daily  weather  map. 

While  many  in  Oregon  are  making  a  practical  use  of  this  information 
to  the  advancement  of  their  business,  there  are  many  who  are  ignorant  of 
the  purpose  for  which  they  are  issued.  It  is  to  enable  this  class  to  make  a 
money  value  through  increased  knowledge  of  the  daily  actual  and  probable 
weather  changes  that  these  charts  are  offered.  This  information  is  of 
especial  utility  to  the  farmer,  as  well  as  to  the  commercial  classes  in  the  city. 

In  the  study  of  these  charts  it  must  be  remembered  that  the  arrows  fly 
with  the  wind.  The  first  four  figures  to  the  right  of  a  station  denote  the 
reading  of  the  barometer;  the  figures  above  the  barometer  figures  denote 
temperature;  the  wind  velocity  and  precipitation  figures  are  below  the  barom- 
eter. The  letter  "S"  at  a  station  denotes  snow,  and  the  letter  "R"  denotes 
rain;  a  cross  denotes  cloudy;  one  mark  indicates  fair,  and  the  absence 
of  characters  or  marks  means  clear  weather.  The  lines  in  the  chart  connect 
places  of  equal  barometric  pressure,  and  are  drawn  to  each  tenth  of  an  inch. 

A  WINTER  STORM. 

Chart  No.  1  shows  a  typical  winter  storm,  though  there  are  some  extreme 
features.  The  terms  "low"  and  "high,"  which  are  used  in  the  description 
of  weather  types,  are  used  to  describe  the  condition  of  the  atmospheric 
pressure  as  reading  low  or  high.  In  Chart  No.  1  the  "low"  is  off  the  Wash- 
ington Coast,  and  the  "high"  is  over  the  British  Possessions.  They  rep- 
resent areas  of  low  and  high  atmospheric  pressure.  The  "low,"  representing 
an  area  of  low  atmospheric  pressure,  is  necessarily  the  center  of  the  storm. 
The  "high,"  representing  the  territory  where  the  barometric  pressure  is 
great,  is  generally  an  indication  of  fair  weather  influence. 


NORTH    PACIFIC    SLOPE. 


21 


As  regards  the  wind  circulation  about  the  areas  of  low  and  high  pressure, 
in  the  Northern  Hemisphere  they  blow  spirally  inward  and  around  the 
"low,"  opposite  to  the  movement  of  the  hands  of  a  watch,  and  they  blow 
outward  from  the  "high."  The  first  is  a  cyclonic  and  the  latter  an  anti- 
cyclonic  movement. 

Chart  No.  1  shows  that  this  law  is  being  obeyed,  except  where  interven- 
tion of  the  mountains  makes  a  change. 


(Chart  No.   1.) 

During  the  winter,  storms  seek  a  low  latitude.  The  well-beaten  track  of 
the  winter  stoim  is  between  latitude  45  and  50,  where  they  strike  the 
Pacific  Coast.  From  the  Pacific  Coast  they  usually  move  somewhat  to  the 
northeastward  for  about  a  thousand  miles,  and  then  southeastward  toward 
the  Great  Lakes. 

This  type  of  storm  is  frequent  on  the  Pacific  Coast.  Its  presence  means 
continued  stormy  weather,  with  rain  and  snow  to  the  west  of  the  Cascades 
in  Washington  and  Oregon,  while  in  the  mountains  and  elevated  districts  of 
Oregon,  Washington,  and  Idaho,  snow  invariably  follows.  The  presence 
of  the  "high"  over  the  British  Northwest  means  that  the  "low"  or  storm 
which  is  located  on  the  coast  will  receive  its  supply  of  cold  air  from  that 
source.  The  tendency  of  the  "high"  is  toward  checking  the  eastern  progress 
of  the  "low."  Since  all  storms  move  from  a  westerly  to  an  easterly  point, 


22  \\ '  MA  Til  KB    TYl'KS. 

the  "high"  in  Chart  No  1,  preceding  the  storm,  acts  as  a  barrier,  causing 
the  "low"  to  remain  nearly  stationary  on  the  coast.  One  of  the  character- 
istics of  a  winter  "low"  whose  progress  is  checked  by  a  "high"  is  to  develop 
energy.  With  the  disappearance  of  a  "high"  to  the  east,  the  general  course 
of  the  "low"  is  to  follow.  In  the  present  case,  the  "low"  of  February  19 
moved  south  into  California,  thence  east.  Such  a  movement,  owing  to  its 
infrequency,  is  erratic,  "Highs"  that  continue  permanent  in  the  British 
Northwest  have  the  tendency  to  force  the  "lows"  southward.  The  reading 
of  the  barometer  vas  abnormally  high  over  the  British  Northwest  for 
several  days,  which  resulted  in  the  storm  being  gradually  forced  south. 

The  most  marked  feature  of  the  weather  that  follows  the  movement  of 
all  storms  from  the  North  Pacific  Coast  States  southward  is  the  cold 
northerly  winds.  While  the  storm  or  "low"  remains  central  on  the  coast, 
the  "high"  acts  as  a  feeder;  the  cold  air  from  the  "high"  rushing  into  the 
field  of  moisture  surrounding  the  "low"  causes  snow.  With  the  disappear- 
ance of  the  "low"  southward  through  the  influence  of  the  "high,"  the  tem- 
rerature  equalizes  and  the  snow  ceases.  The  relative  weight  or  energy  of 
areas  of  low  and  high  barometric  pressure  is  taken  into  consideration  in 
determining  their  probable  course.  It  is  in  this  way  that  forecasts  are 
made,  and,  though  the  layman,  who  makes  a  study  of  the  charts,  may  not 
possess  the  skill  of  an  expert,  yet  he  is  able,  by  conscientious  study  of  the 
weather  charts,  to  make  satisfactory  forecasts. 

CHINOOK  CONDITIONS. 

Chart  No.  2  represents  conditions  most  favorable  to  Chinook  winds. 
It  is  generally  considered  by  the  people  living  in  the  States  of  Oregon, 
Washington,  and  Idaho  that  the  word  "Chinook,"  applied  to  wind,  means 
any  warm  southerly  wind,  whether  it  be  dry  or  moist.  It  is  thought  by 
many  that  the  direct  influence  which  produces  the  wind  comes  from  the 
ocean.  This  is  a  grave  mistake.  Chart  No.  2  shows  the  controlling  influence 
to  be  an  area  of  high  barometric  pressure  over  Nevada,  Utah,  Colorado, 
Wyoming,  Idaho,  and  the  portions  of  Washington  and  Oregon  lying  east 
of  the  Cascades.  The  center  of  this  great  field  of  high  pressure  is  over 
Northern  Nevada,  Southern  Idaho,  and  Northern  Utah.  From  the  center  the 
greatest  influence  will  be  exerted.  Chart  No.  2  shows  the  temperature  on 
the  morning  of  January  9,  1894,  as  follows:  Roseburg,  34°;  Portland,  34°; 
Fort  Canby,  38°;  Seattle,  32°;  Walla  Walla,  28°;  Spokane,  14°;  Helena,  10°; 
Miles  City,  — 6°;  Havre,  20°;  and  Bismarck,  — 22°.  Twenty-four  hours  later 
the  records  at  Portland  showed  the  temperature  to  be  as  follows:  Rose- 
burg,  44°;  Portland,  42°;  Fort  Canby,  42°;  Seattle,  40°;  Walla  Walla,  46°; 
Spokane,  34°;  Helena,  38°;  Miles  City,  40°;  Havre,  32°;  and  Bismarck,  32°. 

It  will  be  observed  that  the  rise  in  temperature  in  twenty-four  hours  was 
as  follows:  Roseburg,  10°;  Portland,  8°;  Fort  Canby,  4°;  Seattle  8°; 
Walla  Walla,  18°;  Spokane,  20°;  Helena,  28°;  Miles  City,  46°;  Havre,  12°; 
and  Bismarck,  54°.  In  this  case,  as  in  all  other  cases  when  Chinook  winds 
are  produced,  the  area  of  high  pressure  is  located  as  stated  above,  while  a 
low  area  or  storm  is  passing  over  the  British  Northwest.  The  greater  the 


NORTH    PACIFIC    SLOPE.  2O 

rapidity  of  the  storm,  the  higher  the  wind  velocity  and  the  temperature 
become. 

The  principle  involved  is  simple.  The  storm  in  passing  over  the  north 
causes  an  indraught  of  the  air  from  the  "high"  toward  the  "low."  In  the 
Columbia  and  Walla  Walla  Valleys,  and  the  passes  of  the  Blue  Mountains, 
Chinook  winds  are  usually  of  a  pronounced  type,  while  under  the  same 
conditions  they  are  moderate  in  the  valleys  of  Western  Oregon  and  West- 
ern Washington.  Though  moderate  and  moist,  they  are  nevertheless 
Chinook  winds. 


(Chart  No.  2.) 

Were  it  possible  to  trace  the  course  and  measure  the  temperature  of  a 
cubic  foot  of  air  that  drifts  from  the  "high"  in  Northern  Nevada  toward 
a  "low"  in  British  Columbia,  we  would  notice  a  rise  in  temperature  of  1.6° 
for  every  300  feet  of  descent  (called  dynamic  heating)  from  the  high  plains 
of  Nevada  to  nearly  sea  level,  where  it  would  reach  the  Willamette  Valley, 
for  this  would  be  its  course. 

When  reaching  the  Willamette  Valley,  where  the  local  atmosphere  would 
be  cool  and  moist,  condensation  would  take  place,  since  the  dynamically 
heated  air  would  be  warmer.  During  the  time  the  process  of  condensation 
is  going  on  in  the  western  portions  of  Oregon,  the  storm  would  be  passing 
over  the  British  Northwest,  and  its  center  would  have  changed  to  Alberta, 


24  WEATHER    TYPES, 

in  which  case  there  would  be  a  rush  of  air  through  the  gorges  of  the 
Columbia  River,  and  over  the  Cascades  toward  the  storm  center.  This 
cubic  foot  of  air  would  undergo  another  change;  ip.  passing  over  the  Cas- 
cades, most  of  its  moisture  would  be  lost  in  condensation,  by  the  meeting 
of  the  cooler  currents  on  the  higher  elevation.  By  the  time  this  air  would 
have  fallen  to  the  plains  &nd  valleys  of  Eastern  Washington  and  Idaho  it 
would  not  only  be  warmed  through  its  descent  but  dry  through  condensa- 
tion of  its  moisture.  It  is  in  thjs  way  that  the  great  flow  of  air  from 
the  "high"  to  the  "low"  produces  the  balmy  but  moist  Chinook  wind  in 
the  valleys  of  Western  Oregon  and  Western  Washington,  and  the  warm 
and  dry  Chinook  to  the  east  of  the  Cascades.  The  farther  the  wind  pro- 
gresses to  the  east,  the  warmer  and  drier  it  becomes,  the  principles  of 
dynamic  heating  of  the  air  being  most  perfect  as  the  air  flows  over  the 
Bitter  Root  Mountains  into  Montana.  In  Montana  and  the  Dakntas  the 
Chinook  is  a  westerly  \vind,  and  its  dryness  and  ability  to  absorb  snow 
or  other  moisture  is  compared  with  the  Foehn  wind  of  the  Alps.  In  explana- 
tion of  the  conditions  represented  in  the  chart  the  area  of  high  pressure  was 
formed  through  the  conjunction  of  two  areas  of  high  pressure,  one  moving 
south  from  the  British  Northwest,  and  the  other  moving  east  from  the 
California  Coast.  This  movement  is  shown  by  the  records  of  the  U.  S. 
Weather  Bureau  on  January  8th,  1894,  the  movements  being  especially 
rapidly.  The  "low"  first  made  its  appearance  during  the  afternoon  and  night 
of  the  8th,  and  arrived  at  its  position,  as  shown  by  the  chart,  by  the 
morning  of  the  9th.  The  "low"  continued  moving  rapidly  toward  the  Great 
Lakes,  and  the  effects  of  the  Chinook  continued  in  Oregon  and  Washington 
for  twenty-four  hours.  Without  the  presence  of  the  "high,"  the  "low"  would 
probably  have  moved  south  and  resulted  in  freezing  temperatures  instead  of 
the  balmy  Chinook.- 

FIRST  WINTER   STORM. 

The  first  "Winter  low"  of  the  fall  season.  By  this  is  meant  the  first 
storm  in  the  fall  season  which  appears  on  the  coast  and  follows  the  track 
usually  followed  by  storms  in  the  winter  season. 

The  difference  between  an  early  and  a  late  fall  is  in  the  date  on  which  a 
storm  of  such  a  chaiacter  first  makes  its  appearance  on  the  coast.  In  the 
summer  season  storms  of  the  character  of  the  North  Pacific  Coast  winter 
storms  move  eastward  at  a  latitude  too  far  north  to  influence  the  weather 
of  the  Pacific  Coast  of  the  United  States;  with  the  approach  of  the  fall 
season  these  storms  seek  a  lower  latitude  in  search  of  heat,  one  of  the 
essential  attributes  of  a  storm.  As  the  conditions  which  cause  one  storm  to 
seek  a  lower  latitude  are  still  present,  other  storms  are  influenced  in  the 
same  direction,  resulting  in  a  succession  of  storms. 

Chart  No.  3  shows  three  "lows,"  or  stages  of  practically  one  storm,  in 
progress  around  an  area  of  high  atmospheric  pressure.  This  is  a  type  of 
weather  common  to  the  fall  and  winter  seasons.  It  is  not  unusual  that 
three  "lows"  appear  on  a  single  daily  weather  chart,  covering  1,500  miles  to 
the  east  of  the  Pacific  Coast  line. 


NORTH    PACIFIC    SLOPE. 


25 


The  chart  represents  an  area  of  high  barometric  pressure  prevailng  over 
California,  Nevada,  Utah,  Southern  Idaho,  and  Southern  Montana.  Anti- 
cyclonic  winds  are  blowing  out  from  the  area  of  high  pressure  toward  the 
"lows"  or  storms.  A  brisk  to  high  southeasterly  wind  is  blowing  in  Oregon 
and  Washington,  while  a  severe  southwesterly  gale  is  raging  at  the  mouth 
of  the  Columbia  River  and  along  the  Washington  Coast. 


(Chart  No.  3.) 

Heavy  rain  is  falling  in  all  portions  of  Western  Washington,  while  light 
rain  is  falling  in  Eastern  Washington  and  Western  Oregon.  The  "low" 
or  storm,  which  is  represented  as  central  about  Tatoosh  Island,  Washington, 
is  the  immediate  cause  of  the  weather  prevailing  in  Oregon  and  Washington. 
Each  of  the  "lows"  represented  on  the  chart  as  preceding  the  one  which  is 
central  on  Tatoosh  Island  had  its  center  at  or  about  Tatoosh  Island,  twenty- 
four  and  forty-eight  hours  before,  respectively.  The  only  one  of  the 
storms  which  is  instrumental  in  influencing  the  weather  on  the  coast  is 
the  Tatoosh  Island  "low";  the  others  have  passed  to  the  east,  where  there  is 
little  moisture  or  heat  to  continue  the  development  and  activity  peculiar  to 
the  position  on  the  coast. 

Since  the  field  of  supply  of  air  necessary  to  continue  the  storm  in  activity 
is  to  the  south  and  southeast,  it  is  essential  in  order  to  continue  the  perfect 
and  regular  storm  progression  that  the  "high"  or  base  of  air  supply  should 


26  WKATHKR    TYI'KS. 

not  become  exhausted.  With  the  exhaustion  of  the  high-pressure  area  on 
the  south  and  southeast,  the  regular  storm  progression  as  shown  on  the 
chart  disappears  the  winds  on  the  coast  and  interior  abate  their  fury, 
the  precipitation  assumes  a  different  character,  and  the  temperature  becomes 
much  colder. 

Storm  No.  3  first  made  its  appearance  on  the  coast  in  the  afternoon  and 
evening  of  October  28th,  and  was  noted  in  the  morning  daily  weather  chart 
at  Portland  as  typical  of  the  first  appearance  of  a  winter  storm.  It  was 
attended  by  gales  on  the  coast,  ranging  from  40  to  60  miles  an  hour,  and 
having  heavy  rain  in  the  western  portions  of  Washington  and  the  north- 
western portions  of  Oregon.  From  the  conditions  represented  by  Chart 
No.  3,  storms  continued  to  appear  over  Northwestern  Washington  at  reg- 
ular intervals  of  twenty-four  hours  until  the  2d  of  November,  when  an 
area  of  high  barometric  pressure  of  exceptional  dimensions  appeared  on 
the  California  Coast,  and,  moving  northward,  caused  the  storms  on  the 
north  to  seek  a  higher  latitude. 

Since  eight  to  twelve  hours  of  temporary  clearing  weather  follow  a 
storm  after  it  has  taken  an  easterly  course,  study  of  the  above  conditions 
would  tend  to  explain  why  apparently  good  local  signs  of  fair  weather  are 
so  soon  followed  by  stormy  weather. 

THUNDER  STORM. 

Chart  No.  4  was  made  from  conditions  which  prevailed  on  the  morning 
of  June  3,  1894,  at  5  A.  M.,  local  time,  and  is  selected  to  represent  typi- 
cal thunder-storm  conditions.  Frequent  and  severe  thunder  storms  occurred 
on  the  2d,  3d  and  4th  of  June,  1894,  in  many  portions  of  Washington,  Ore- 
gon and  Idaho.  The  above  map  also  represents  the  conditions  preceding 
the  occurrence  of  a  tornado  of  unusual  severity  at  11  o'clock  on  the  morning 
of  June  3,  at  Long  Creek,  Grant  County,  Oregon,  the  only  tornado  occur- 
ring in  the  State  of  which  there  is  an  official  record.  In  the  Northwest  Pacific 
Coast  territory,  embracing  the  States  of  Oregon,  Washington,  and  Idaho,  thun- 
der storms  attend  the  advancement  of  areas  of  low  barometric  pressure  which 
have  their  origin,  as  a  rule,  in  the  northern  interior  portions  of  California. 
These  areas  of  low  pressure  are  the  result  of  excessive  heat  in  Northern  and 
Central  California,  the  temperature  frequently  rising  to  104°  to  108°  and 
remaining  warm  for  many  consecutive  days.  Two  or  three  days  of  excessive 
warm  weather  usually  suffices  to  produce  a  local  barometric  depression. 
These  areas  of  low  pressure  advance  northward  into  Southern  Oregon,  thence 
easterly  into  Eastern  Oregon  and  Southern  Idaho,  or  northeasterly  inio  East- 
ern Oregon,  Eastern  Washington,  and  Northern  Idaho.  With  the  advancement 
of  the  areas  of  low  pressure  the  area  covered  by  them  increases.  While  the 
conditions  most  productive  of  thunder  storms  have  their  origin  more  fre- 
quently in  California,  the  rule  is  not  unvarying.  On  June  2  and  3,  1894, 
through  the  agency  of  excessive  heat  throughout  Oregon,  portions  of  Nevada 
and  Washington,  an  area  of  low  barometric  pressure  was  formed  over  Oregon 
which  caused  general  thunder  storms  and  furnished  the  data  for  the  chart 
presented  herewith. 


NORTH    PACIFIC    SLOPE. 


27 


Thunder  storms  are  frequent  in  Eastern  and  Southern  Oregon,  Eastern 
Washington,  and  in  Idaho.  They  rarely  occur  in  the  western  portions  of 
Washington,  and  Northwestern  Oregon.  The  rarity  of  thunder  storms  is 
so  marked  in  sections  of  Western  Washington  and  Northwestern  Oregon  that 
season  after  season  passes  without  so  much  as  a  distant  peal  of  thunder  being 
heard. 


(Chart   No.  4.) 

Thunder  storms  arc  more  frequent  during  the  months  of  June  and  July 
than  at  any  other  time,  and  are  almost  invariably  attended  by  severe  hail 
of  a  character  to  damage  crops,  and  at  times  imperil  the  lives  of  grazing 
animals.  Owing  to  the  small  area  covered  by  a  thunder  storm,  several  have 
been  known  to  be  raging  at  the  same  moment  within  a  single  barometric 
depression;  for  this  reason  thunder  storm  forecasting  is  unsatisfactory  work. 
That  a  thunder  storm  will  occur  somewhere  within  an  area  of  low  pressure 
within  a  specified  time  can  be  forecasted  with  great  accuracy,  but  the  exact 
position  of  the  storm  within  the  area  of  low  pressure  is  a  more  difficult  prob- 
lem, and  one  which  requires  the  light  of  more  frequent  telegraphic  reports 
at  a  greater  number  of  reporting  stations. 


28 


WEATHER   TYPES, 


SUMMER    WEATHER    CONDITIONS. 

Chart  No.  5  represents  the  appearance  of  the  first  summer  "high"  on  the 
Pacific  Coast  during  the  season  of  1896.  Study  of  Pacific  Coast  weather  types 
has  determined  that  there  is  a  well-defined  area  of  high  barometric  pressure 
which  appears  on  the  North  California  or  Oregon  Coast  sometimes  in  the 
spring  or  early  summer,  which,  by  a  characteristic  northerly  movement,  is 
indicative  of  a  decided  change  about  to  commence  in  the  general  character 
of  the  weather  for  the  remainder  of  the  season.  It  is  important  for  the 


7         ~*?\ -C. & Dqartmeirt of  Agricnllore  WaUberJUp.  I  , 


(Chart  No. 


student  of  the  weather  or  one  whose  business  is  affected  by  weather  changes, 
to  know  that  such  a  distinguishing  feature  of  the  weather  develops  each 
spring,  and  by  access  to  the  Daily  Weather  Maps  furnished  by  the  United 
States  Weather  Bureau  its  appearance  can  be  ascertained.  It  is  important 
for  him  to  know  that  there  is  a  type  of  weather  which  develops  each  spring 
and  which  marks  the  time  between  winter  and  summer. 

It  is  to  be  understood  that  when  the  "summer  high"  appears  a  change 
in  the  weather  of  a  summer-like  character  is  about  to  commence;  this  is 
quite  certain,  whether  the  high  appears  in  March  or  in  June.  It  is  not  to 


NORTH    PACIFIC    SLOPE.  29 

be  understood  that  with  the  appearance  of  the  "high"  the  rains  will  cease, 
but  that  the  rains  will  be  more  showery  and  less  frequent.  Increase  in  the 
amount  of  sunshine,  higher  temperatures,  and  more  frequent  periods  of  fair 
weather  should  follow  the  first  appearance  of  a  "summer  high."  With  the 
appearance  of  the  "summer  high"  general  and  prolonged  spells  of  rainfall 
should  cease  and  temperatures  normal  or  above  should  follow. 

Chart  No.  5  was  made  from  conditions  which  existed  on  the  morning  of 
June  13,  1896.  The  "high"  is  represented  as  prevailing  over  Western  Wash- 
ington, extending  westward  along  latitude  48°  north.  This  "high,"  which 
is  considered  typical  of  summer,  moved  from  the  southwest,  showing  first  on 
the  California  Coast.  It  continued  moving  north  along  the  coast  in  British 
Columbia,  thence  easterly;  which  is  the  movement  typical  of  the  "summer 
high"  which  distinguishes  it  from  the  "highs"  of  the  winter  season  that 
appear  on  the  California  Coast,  move  northward  to  about  latitude  45°,  thence 
east  to  the  North  American  plateau,  where  their  progress  is  frequently 
checked. 

In  the  spring  of  1895,  the  "summer  high"  appeared  on  April  20th;  the 
character  of  the  weather  then  changed  and  farming  operations  progressed 
with  only  slight  interruptions  from  the  weather.  In  the  spring  of  1896  the 
"summer  high"  not  having  appeared  until  June  13th,  the  season  was  consid- 
ered six  weeks  late,  farming  operations  were  impeded  by  rain,  and  seed 
decayed  in  the  ground,  owing  to  the  cool  weather. 

Knowledge  concerning  this  feature  of  Pacific  Coast  weather  is  of  incal- 
culable value,  since  it  may  be  regarded  as  the  initial  sign  of  spring. 


INDEX. 


Abbe,  Prof.  Cleveland 9 

Blandford,  S.  M 2, 20 

Chart  No.  i  (A  Winter  Storm) 21 

Chart  No.  2  (Chinook  Conditions) 23 

Chart  No.  3  ( First  Winter  Storm) 25 

Chart  No.  4  ( Thunderstorm) 27 

Chart  No.  5  (  Summer  Weather  Conditions) 28 

Chinook,  Definition  of  Term -*z  10 

Chinook  Conditions 22 

Chinook  Winds 7, 10, 22 

Forecasts,  Long-Range 8 

Forecasting  Weather 3 

Moore,  Prof.  Willis  L i 

Pague,  B.  S 2, 3, 8, 16 

Preface 2 

Sensible  Temperatures 16 

Summer  Conditions 13, 28 

Thunderstorm 13, 26 

Weather  Forecasting 3 

Weather  Maps 14 

Weather  Types 6, 20 

Winter  Conditions 13 

Winter  Storm 20 

Winter  Storm,  First 24 


UNIVEKSTTY  OF  CALIFORNIA  LIBRARY, 
BERKELEY 

THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


? 

,-xpi  ration   <»f  loan  period. 


.. 


' 


10m-4,'23 


23 

Ai* 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


